Always best to find a good reputable agent, preferable a cruise specialist, that you feel comfortable with. Keep in mind that most of the mass market cruise lines requires everyone to advertise the same cruise for the same price. Plus, a good agent will not charge any fees.
I don't suggest booking directly with the cruise line because if you have any problems, who do you think they represent? I'm also not a fan of these large online sites because staff is constantly changes.
In fact, there was a report once put out by an industry organization where their investigations found when calling the cruise line or a large online site, the people answering the phone were; 1) working in a call center, 2) were not certified travel agents, 3) had worked for the company less than 6 months, and 4) had never even seen a ship let alone been on a cruise or to any of the ports, so their knowledge was limited to selling and not in providing any helpful information.
With that said, do what you're doing - look for recommendations. Check out their website; is it professional looking? What are their office hours? Can you get ahold of them 24-7 in an emergency? Give the agent a call and talk to them - ask alot of questions. Do they answer the phone right away? Find out how long they've been in business, how many cruises they've been on, what cruise lines have they been on, what ships, where they've cruised, etc. One important question to ask is do they sell Royal Caribbean cruises? If the answer to that question is no, run the other way. RCCL is the first to yank agent's credentials for not abiding by their policies. Also, ask if they charge your credit card or whether they have the cruise line charge your credit card. If they charge it, again, run the other way. You only want to do business with agencies who have the cruise line charge your credit card.
No matter what you decide, definitely find a reputable agent that you feel comfortable with and can talk to and is available when you need them. An agent can be worth their weight in gold, especially if you have any problems, so you want someone who will be on your side and fight any battles for you if needed.
As Warren Buffet said, "Price is what you pay. Value is what you get." A good agent is more interested in getting your business, not in just getting your money.
Hope this helps.